BY 32 – SPRING 2002
Study Outline
15.1. Comparison of Cardiac and Skeletal Muscle:
a. Like skeletal muscle, cardiac muscle cells contain actin and myosin organized into _____________________________________ and contract in response to ___________________________________. Contraction in both cell types is dependent on an increase in intracellular _______________________________________.
b. In cardiac muscle, the action potential is generated by ___________________ cells and passes from cell to cell via _________________________________.
c. Skeletal muscle is voluntary whereas cardiac muscle is _____________________________.
d. The duration of action potentials in skeletal muscle is on the order of _________________________________ whereas in cardiac muscle, it is on the order of ____________________________________.
15.2. Action Potential of a Cardiac Contractile Cell:
a. The resting potential of a typical contractile cell is on the order of _______________________________ and is attributable to relatively high permeability to ___________________________ and low permeability to _____________________________.
b. When the fiber is brought to threshold by excitation from a neighboring cell, _____________________________ open which increases Na+ permeability. As a result the membrane potential approaches ______________________.
c. The plateau phase of the action potential is attributable to _______________________________ and __________________________. The Ca2+ influx is due to opening __________________________________.
d. Repolarization of the cell is due to an increase in _________________________________, while at the same time a decrease in ____________________________ and ______________________________.
e. The heart cannot develop tetanus because the __________________________ period is longer than the duration of contraction. Tetanus would be harmful to cardiac function because the heart must ______________________________ between contractions so as to allow filling.
15.3. Action Potential of a Cardiac Conducting Cell:
a. Cells which are capable of spontaneously generating action potentials in the heart are called _____________________________________ and form the _____________________________________.
b. Through the presence of pacemaker cells, the heart is able to initiate action potentials in the absence of _____________________________________ and ________________________________. The ability of the heart to generate a pattern of action potentials is called _________________________________.
c. In conducting cells there is no real resting potential but instead the most negative potential is called the _____________________________________.
d. The pacemaker potential refers to the slow depolarization that is due to ________________________________ which causes the membrane potential to increase to _______________________________.
e. Unlike contractile cells, the upstroke of the action potential is attributable to an influx of _________________________________.
f. Repolarization is due to an increase in _____________________________ and a decrease in ___________________________________.
15.4. The Conduction System:
a. Normally the fastest rate of spontaneous depolarization occurs in the _______________________________ which then paces the entire heart. This pattern is called _____________________________________.
b. The SA node is located at the junction of the ________________________ and ________________________________ and consists of conducting cells embedded in a mass of __________________________________________.
c. The preferred path between the SA and AV node is called the ___________________________________________.
d. The AV node is located just deep to the endocardium of the _____________________________________ in the base of the ______________________________________.
e. Because of the small diameter of conducting cells within the AV node, the action potential is delayed, a phenomena called the _____________________.
f. Leaving the AV node is the __________________________________ which proceeds to split into _______________________________________ which then become a network of ________________________________________.
g. Within the ventricles, the _______________________________ contract first, followed by the _____________________________________, and finally the _______________________________.
h. Defects in the intrinsic conduction system of the heart cause irregular heart rhythms called ________________________________________. When as a result, the heart undergoes rapid irregular contractions, this condition is called ________________________________________.
i. When pacing of the heart comes from somewhere other than the SA node, this is called an _____________________________________.
15.5. The EKG:
a. The EKG is obtained from surface electrodes which measure ___________________________________ that result from action potential propagation through the heart. The wave of depolarization is reflected as a wave of __________________________________ whereas repolarization is reflected as a wave of _______________________________.
b. The P wave represents _________________________________________. At the top of the peak about ____________________________ the atrium is depolarized.
c. The QRS complex represents ____________________________________. The time between the end of the P wave and the beginning of the QRS represents the time spent in the __________________________________, ____________________________, and ____________________________.
d. The T wave represents ________________________________. Atrial repolarization is hidden by the __________________________________.
e. The S-T segment represents the time period in which the ventricular contractile fibers are ___________________________________ during the ___________________________________ phase of the action potential.
f. The _______________________________ can be used to compute heart rate. Rates faster than normal are called ___________________________ whereas rates slower than normal are called __________________________________. A typical heart rate in normal sinus rhythm is about ___________________________________.
g. Atrial fibrillation is indicated by a lack of _________________________ whereas the uncoordinated random fluctuations of an EKG most likely indicate ____________________________________.
15.6. Excitation-Contraction Coupling:
a. During the plateau phase of the action potentials _______________________ enters the cell which in turn stimulates _______________________________.
b. Contraction occurs when Ca2+ binds to ______________________________ allowing cross bridge formation to occur.
c. Relaxation occurs when cytosolic Ca2+ levels are reduced through the action of the ____________________________, ____________________________, and ______________________________.
d. Mechanisms which lead to an increase in cytosolic Ca2+ result in an _____________________________. Examples include sympathetic nerves, ________________________________ and certain other hormones. Another class are the _____________________________ such as digitalis which act to inhibit the ___________________________ which leads to an ____________ in intracellular Na+.
e. Agents which increase the strength of contraction are called positive _____________________________ agents.
15.7. The Cardiac Cycle:
a. The ________________________________ refers to all the events associated with the flow of blood through the heart during one complete heartbeat.
b. The period known as __________________________________ is when the ventricles are relaxed and both the ___________________________ and the ____________________________ are closed. As ventricular pressure falls below _____________________________, the mitral valve opens.
c. Ventricular filling is most rapid during the ___________________________ stage but slows during the phase known as ___________________________. In both, the atria and ventricles are relaxed, a condition known as _________________________________.
d. During atrial systole, the ventricular volume increases to __________________________________
e. During ventricular systole as the pressure in the LV exceeds the LA, the _______________________________________ closes giving rise to the ___________________________________ heart sound. At this point the left ventricle is in ________________________________.
f. Once the pressure in the LV exceeds that in the aorta, the ___________________________________________ opens giving rise to ___________________________________________.
g. As the LV begins to relax (onset of the ______________________ wave), the pressure in the ventricle falls below aortic and the _____________________ closes, giving rise to the _________________________________________.
h. The volume of blood left in the ventricle is called the _______________________________________. By contrast the volume of blood ejected in one cardiac cycle is called the ______________________________________________ and is equal to the _______________________ minus the _____________________________.